1. Field of the Invention:
The invention relates in general to particulates, and in a preferred embodiment to superconductor powder and methods of improving its electrical characteristics.
2. Description of the Prior Art:
U.S. Pat. No. 4,411,959, which is assigned to the same assignee as the present application, discloses superconductor wire fabrication techniques which utilize a submicron-particle size powder selected from any superconducting material that can be synthesized in the form of ultrafine micro-powder. The superconductor powder, which may be produced by hydrogen plasma reaction, as set forth in U.S. Pat. No. 4,050,147, or by co-reducing a mixture of metal halides with liquid alkali metal, as disclosed in U.S. Pat. No. 4,419,125, should have a particle size of less than 1,000 angstroms, with significant contribution from 100 angstrom sizes.
For optimized superconducting properties, there should be direct physical contact between the surfaces of the adjacent particles during wire fabrication, with no intervening layers of surface oxide between the particles. A superconductor compound which includes niobium is a preferred material in the superconductor wire of the hereinbefore mentioned U.S. Pat. No. 4,411,959, such as niobium carbide (NbC), niobium aluminide (Nb.sub.3 Al), niobium carbonitride (NbCN) niobium stannide (Nb.sub.3 Sn) and ternary variations such as Nb.sub.3 (Al,Ge). It has been found that particulates of such niobium compounds, especially NbC and NbCN when prepared by plasma techniques, are covered by a tenacious film of niobium oxide (Nb.sub.2 O.sub.5) about 10 angstroms thick. It would thus be desirable to not only remove the niobium oxide prior to wire fabrication, but to preserve a pristine surface on the superfine superconductor particles right up to the point of powder encapsulation in a tube which starts the wire fabrication process.